class Screen(object):
    @property
    def width(self):
        return self._width

    @width.setter
    def width(self,value):
        self._width = value

    @property
    def height(self):
        return self._height

    @height.setter
    def height(self,value):
        self._height = value

    @property
    def resolution(self):
        return self._height*self._width

s = Screen()
s.width = 4
s.height = 3
print('resolution = ', s.resolution)